Recently, a virtualization technique that integrates and manages logical volumes in each storage apparatus installed at each of a plurality of sites and logical volumes under control of different storage apparatuses and provides a host system with the logical volumes as virtual logical volumes (hereinafter referred to as the virtual volumes) existing under control of one virtual storage apparatus (hereinafter referred to as the virtual storage apparatus) has been suggested and put to practical use.
Such a virtualization technique assigns a unique virtual apparatus number to each storage apparatus in a computer system and maps each logical volume existing in each storage apparatus to any of virtual volumes existing in the virtual storage apparatus. Then, only the virtual storage apparatus and virtual volumes provided by the virtual storage apparatus are provided to the host system.
The above-described virtualization technique has the advantage that a system administrator can manage the logical volumes in the computer system without recognizing the storage apparatuses in the computer system or the logical volumes defined in the storage apparatuses.
On the other hand, data backups using a replication copying (real-time copying) technique have been widely employed in recent years particularly in computer systems of large-scale companies and governments in order to protect data against large-scale natural disasters such as earthquakes or hurricanes, human-caused disasters such as disasters caused by erroneous operations by the system administrator or terrorism attacks, and data destruction caused by failures of equipment and programs.
Examples of such replication copying include local copying, snapshots, and remote copying. Local copying is data copying within the same storage apparatus and remote copying is data copying between storage apparatuses. Furthermore, snapshots are static data images of logical volumes at the time of acquisition of the snapshots. When a snapshot is obtained in a storage apparatus, to which the snapshot technique is applied, and data is then written to the relevant logical volume, data immediately before that write data is written (data at the time of snapshot acquisition) is saved to another logical volume. Therefore, the logical volume at the time of snapshot acquisition can be restored by combining the data at the time of snapshot acquisition remaining in that logical volume and the data saved to another logical volume.